Comment by mcepl
I don’t think it is that simple. Itanium was for years supported for example by RHEL (including GCC working of course, if anybody cared enough they could invest into optimising that), it is not like the whole fiasco happened in one moment. No, Itanium was genuinely a bad design, which never got fixed, because it apparently couldn’t be.
Well, yes, the market didn't care all that much for various reasons. (There were reasons beyond technology.) RHEL/GCC supported but, while I wasn't there at the time, I'm not sure how much focus there was. Other companies were hedging their bets on Itanium at the time--e.g. Project Monterey. Aside from Sun, most of the majors were placing Itanium bets to some degree if only to hedge other projects.
Even HP dropped it eventually. And the former CEO of Intel (who was CTO during much of the time Itanium was active) said in a trade press interview that he wished they had just done a more enterprisey Xeon--which happened eventually anyway.